1. Field of the Invention
The present invention relates to a liquid container preferably used in the field of ink jet recording or the like, and more particularly to a liquid supply system whose liquid container can be partially replaceable.
2. Related Background Art
Ink tanks have been proposed which apply negative pressure to an ink discharge head. These tanks are most generally designed so that they use capillary force of porous matter. The ink tanks include porous matter, such as sponge, packed, preferably being compressed, in the entire tanks and an air communication port through which air can be taken in the ink container to supply ink smoothly during printing.
A problem with porous matter used as an ink retaining member is low ink containing capacity per unit volume of the porous matter. To solve this problem, the applicant proposed in Japanese Patent Application Laid-Open No. 7-125232 an ink tank with an ink container which is substantially sealed in whole excluding the communication portion against a capillary force generating member container, which tank is used, with the capillary force generating member container open to the air. The applicant also proposed in Japanese Patent Application Laid-Open No. 6-226990 an ink tank configured as described above whose ink container is replaceable.
In the above-described ink tank, ink is supplied from the ink container to the capillary force generating member container by gas/liquid exchange during which gas is introduced into the ink container as ink leaves the container. Thus the ink tank advantageously allows ink to be supplied under almost constant pressure during gas/liquid exchange. Considering its ease of replacement, the ink tank, disclosed in Japanese Patent Application Laid-Open No. 6-226990, is also technically good.
In Japanese Patent Application Laid-Open No. 8-20115, on the other hand, the applicant proposed an ink tank which uses fibers made of a thermoplastic olefin resin (for example, polypropylene and polyethylene) as a capillary force generating member. The ink tank is good at ink storage stability. It is also easy to recycle because the ink tank enclosure and fibers are made of the same material.
An ink tank in which the above-described capillary force generating member container is adjacent to its corresponding ink container performs gas/liquid exchange, that is; introduces gas into the ink container when supplying ink from the ink container, which has a predetermined capacity, to the capillary force generating member container.
Using fibers made of the above-described olefin resin as an ink absorbent, or the capillary force generating member in the capillary force generating member container, has been found to cause bubbles to stagnate in a communication portion when much ink is supplied in a short time.
Analysis of the phenomenon unique to the fiber absorbent by the inventors has shown that the problem is caused by absorbent characteristics described below.
In contrast to conventional porous material, such as urethane foam, ink absorbents using fibers have the following characteristics:
(1) Because these absorbents have a high porosity, pressure loss due to ink movement is small.
(2) The difference between the leading and trailing angles of contact of ink with fibers is small.
(3) Because gaps between fibers produce capillary force, the difference in local capillary force between urethane sponge cells (about 80 to about 120 xcexcm in size) is small, compared with ink absorbents formed by foaming urethane and then removing cell membranes.
Thus a plurality of passages from the air communication port to the communication portion are formed during gas/liquid exchange especially when much ink is supplied in a short time. Because of this, much gas floods into the communication portion, thus causing bubbles to stagnate in the communication portion.
On the other hand, the inventors found another technical problem with an ink tank in which the capillary force generating member container is adjacent to its corresponding ink container, which can be replaced by removing it from the capillary force generating member container.
The problem is that enlarging the cross-portional area of the communication portion between the ink container and the capillary force generating member container to cover a high flow rate of about 10 to about 15 g/min, which rate has not been assumed, may cause air to be taken in the ink container, thus disturbing pressure balance between the ink container and the capillary force generating member container when the ink container is attached to the capillary force generating member housing.
The present invention has been made based on the above-described novel findings. It is a first object of the present invention to provide an ink tank and a liquid supply system which supply ink stably by solving, from a viewpoint different from conventional techniques, the problem of unstable ink supply which occurs due to bubble stagnation in a communication portion at a high ink supply rate per unit time when a fiber absorbent is used as a negative pressure generating member in the ink tank or ink supply system in which a negative pressure generating member container is adjacent to a liquid container.
It is a second object of the present invention, in addition to or independently of the above first object, to provide a liquid supply system which has a simple structure not to make its installation or removal difficult and prevents air to enter an ink supply container when the container is attached to a capillary force generating member container.
It is a third object of the present invention to provide an ink jet recording apparatus using a liquid supply system of the present invention.
To attain the first object, a liquid supply system of the present invention has on the one hand a liquid supply container including a liquid container for storing liquid in a hermetically sealed space and on the other hand a negative pressure generating member container communicating with the above-described liquid container through portions of communication with the liquid supply container and containing a negative pressure generating member and supplies liquid by gas/liquid exchange, that is; by introducing gas through the above-described communication portions into the above-described liquid container and carrying liquid out of the above-described liquid container into the above-described negative pressure generating member container, wherein the above-described communication portions, which number 2, are provided one above the other in the direction of gravitational force.
In the present invention, arranged as described above, the two communication portions provided in the direction of gravitational force allow the liquid supply container including a liquid container for storing liquid in a hermetically sealed space and the negative pressure generating member container containing a negative pressure generating member to communicate with each other. Gas is exchanged with liquid by introducing gas into the liquid container and carrying liquid out of the liquid container into the negative pressure generating member container through these two communication portions. During ordinary liquid supply, gas is exchanged with liquid mainly through the communication portion provided above in the direction of gravitational force if a small amount of liquid is supplied, and only liquid is mainly carried out of the liquid supply container into the negative pressure generating member container mainly through the communication portion provided below in the direction of gravitational force. On the other hand, if a large amount of liquid is supplied, gas moves mainly through the communication portion provided above in the direction of gravitational force while liquid moves mainly through the communication portion provided below in the direction of gravitational force. If one of the communication portions is blocked by stagnant bubbles, gas is exchanged with liquid through the other communication portion. Because gas and liquid are exchanged between the liquid supply container and the negative pressure generating member container using both or either of the two communication portions according to the amount of liquid to be supplied and rate of liquid supply, liquid is stably supplied.
To attain the second object, a liquid supply system of the present invention has on the one hand a liquid supply container for holding liquid in a hermetically sealed space and on the other hand a capillary force generating member container containing a capillary force generating member which can be installed to, or removed from, the liquid supply container and hold liquid,
wherein the liquid supply system has a plurality of connection tubes which connect the liquid supply container and capillary force generating member container together, wherein the plurality of connection tubes include gas/liquid exchange connection tubes positioned above vertically and liquid supply connection tubes positioned below vertically, and wherein earlier than the gas/liquid exchange connection tubes, the liquid supply connection tubes allow the liquid supply container to communicate with the capillary force generating member container when the liquid supply container is installed to the capillary force generating member container.
In addition, the present invention provides an ink jet recording apparatus to which the above-described liquid supply systems apply. An ink jet recording apparatus of the present invention has on the one hand a liquid supply system which has one of the above-described structures and on the other hand a liquid discharge head which sprays liquid supplied from the negative pressure generating member container on a recording medium.